Response of jejunal Na+,K+-ATPase to 5-hydroxytryptamine in young and adult rats: Effect of fasting and refeeding

The present study is aimed to evaluate the effects of 5-hydroxytryptamine ( 5-HT) upon jejunal Na+, K+-ATPase in young (20-day-old) and adult (60-day-o ld) rats, and determine the effect of food intake on the response of the so dium pump to the amine. Basal Na+, K+-ATPase activity in jejunal epithelial cells from young rats was twice that in adult animals and responded to 5-H T with stimulation. In adult rats, fasting reduced by 25% basal jejunal Na,K+-ATPase activity, whereas in young rats, no such change was observed. Th e sensitivity of jejunal Na+,K+-ATPase to 5-HT in young fasted rats was sim ilar to that observed in fed animals. The effect of refeeding in young rats was a 2-fold increase in jejunal Na+, K+-ATPase activity, this being accom panied by insensitivity to 5-HT. In adult rats, refeeding was accompanied b y an increase in jejunal Na+,K+-ATPase activity. It is concluded that the s timulatory effect of 5-HT upon jejunal Na+,K+-ATPase activity is a phenomen on dependent on both age and type of diet. In young rats, it is the food in take that plays an important role in development of insensitivity of Na+,K-ATPase to stimulation by 5-HT, while in adult animals fasting or fasting f ollowed by refeeding does not play a major role in regulating its sensitivi ty to the amine.